JP4879040B2 - Solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor including a valve metal or an anode using a valve metal as a main component, and a dielectric layer formed by anodizing the anode. The present invention relates to a solid electrolytic capacitor that is reduced.

  In general, a solid electrolytic capacitor is formed by forming an oxide layer as a dielectric layer by anodic oxidation on the surface of a valve action metal, forming a cathode layer thereon, and further providing a cathode lead lead from the cathode layer. It has a structure. The valve metal is a group of metals having a valve action, and examples thereof include aluminum, tantalum, niobium, and titanium.

  However, in these solid electrolytic capacitors, crystalline oxides (defects) are formed in the dielectric layer in the step of forming the dielectric layer by anodic oxidation, and cracks are generated at the crystal grain boundaries of the dielectric layer. Such a defect has a problem that resistance is small and a current flows through the defect, so that a leakage current as a solid electrolytic capacitor increases.

  As a factor for forming the defect, an influence of oxygen contained in the valve metal can be considered. For suppression of leakage current, for example, Patent Document 1 describes a nitrogen-containing metal in which nitrogen is dissolved in niobium or tantalum as a metal for an anode of a solid electrolytic capacitor.

However, even when the nitrogen-containing metal described in Patent Document 1 is used as the anode metal of the solid electrolytic capacitor, the leakage current reduction effect is still not sufficient.
JP 2001-223141 A

  This invention is made | formed in view of the above situation, Comprising: It aims at providing the solid electrolytic capacitor with small leakage current.

  The solid electrolytic capacitor of the present invention is a solid electrolytic capacitor comprising an anode, a cathode, and a dielectric layer formed by anodizing the anode, wherein the anode is any one of niobium, aluminum, tantalum, or niobium. A first metal layer made of an alloy containing aluminum, tantalum as a main component, and a part of the surface of the first metal layer is coated with a second metal layer containing any of titanium, zirconium, and hafnium. It is characterized by being.

  In the solid electrolytic capacitor of the present invention, preferably, the area of the region of the first metal layer covered with the second metal layer is not less than 0.5% and not more than 10% of the surface area of the first metal layer. .

  According to the solid electrolytic capacitor according to the present invention, generation of defects in the dielectric layer can be suppressed in the step of forming the dielectric layer by anodic oxidation, and the leakage current of the solid electrolytic capacitor can be reduced. .

  Next, a solid electrolytic capacitor according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. The solid electrolytic capacitor of the present invention is not limited to those shown in the following embodiments, and can be implemented with appropriate modifications within a range not changing the gist thereof.

  FIG. 1 is a schematic cross-sectional view of a solid electrolytic capacitor in this embodiment.

  In the solid electrolytic capacitor in this embodiment, as shown in FIG. 1, the anode 1 is a first metal layer made of niobium, aluminum, tantalum or an alloy containing niobium, aluminum, tantalum as a main component. 2 and a second metal layer 3 containing any one of titanium, zirconium, and hafnium. A part of the surface of the first metal layer 2 is covered with the second metal layer 3. Further, an anode lead 11 is extended from the anode 1.

  According to such a configuration, it is considered that titanium, zirconium, and hafnium, which are the second metal layer, act as a deoxidizer, and oxygen contained in the first metal layer can be reduced. Therefore, even when a dielectric layer 4 described later is formed by anodic oxidation, it is possible to suppress the formation of defects in the first metal layer, so that a solid electrolytic capacitor with a small leakage current can be obtained.

  FIG. 2 is a schematic top view of the anode 1 as viewed from the upper side of FIG. A part of the surface of the first metal layer 2 is covered with the second metal layer 3.

  In the present embodiment, as shown in FIGS. 1 and 2, the region of the second metal layer 3 includes a plurality of rectangular regions on both surfaces of the first metal layer 2, but is not limited thereto. Other shapes such as a line shape and a rib shape may be used. Further, the arrangement of the second metal layer 3 on the first metal layer 2 and the positional relationship of the plurality of second metal layers 3 can be adjusted as appropriate. Furthermore, the region of the second metal layer 3 is preferably dispersed rather than localized on the first metal layer 2.

  The area of the region of the first metal layer covered by the second metal layer is preferably 0.5% or more and 10% or less of the surface area of the first metal layer. When it is less than 0.5%, it is considered that the effect of reducing the oxygen concentration in the first metal layer is relatively small. Moreover, when it exceeds 10%, since the leakage current through the defect formed in the 2nd metal layer surface becomes large, it is thought that the effect of leakage current reduction becomes small as a whole. However, even if a defect occurs on the surface of the second metal layer, the effect of reducing the leakage current by suppressing the occurrence of the defect on the first metal layer is greater. Therefore, even if it exceeds 10%, the leakage current can be reduced as compared with the prior art.

  Then, the anode 1 is anodized in an electrolytic solution, and a dielectric layer 4 made of an oxide is formed on the surface of the anode 1.

  A capacitor element 10 is constituted by the anode 1 and the dielectric layer 4 described above.

  An electrolyte layer 5 is formed so as to cover the surface of the dielectric layer 4. Here, as a material used for the electrolyte layer 5, for example, a conductive polymer material such as polypyrrole, polythiophene, or polyaniline, or a conductive oxide such as manganese dioxide can be used.

  In forming the cathode 6 so as to cover the surface of the electrolyte layer 5, a carbon layer 6a is formed on the electrolyte layer 5 using a carbon paste, and further on the carbon layer 6a, The silver layer 6b is formed using a silver paste.

  In the solid electrolytic capacitor in this embodiment, the anode lead 11 made of nickel plated on iron is connected to the anode lead 11 extended from the anode 1 by welding. A cathode terminal 8 made of iron plated with nickel is connected to the silver layer 6b of the cathode 6 via a conductive adhesive layer 12, and the anode terminal 7 and the cathode terminal 8 are taken out to the outside. Thus, the outer package 9 is made of an insulating resin such as an epoxy resin.

  In the solid electrolytic capacitor of the embodiment shown in FIG. 1, the carbon layer 6a using the carbon paste and the silver layer 6b using the silver paste are stacked as the cathode 6 as described above. It is also possible to provide only the silver layer 6b so as to cover the surface of the electrolyte layer 5 without providing the carbon layer 6a. Moreover, the anode 1 may be comprised from the substantially plate shape, the column shape, etc. which consist of metal foil or a porous sintered compact.

  Next, a solid electrolytic capacitor according to a specific embodiment of the present invention will be described, and in the solid electrolytic capacitor according to the embodiment of the present invention, an increase in leakage current is suppressed by giving a comparative example. To clarify. In addition, the solid electrolytic capacitor of this invention is not limited to what was shown in the following Example, In the range which does not change the summary, it can implement suitably.

Example 1
As the first metal layer 2, a niobium foil having a thickness of 100 μm was used, and a titanium film having a thickness of 0.1 μm was formed on the niobium foil surface by a cathodic arc vapor deposition method. Here, the titanium film was formed under the conditions of a chamber internal pressure of 1 × 10 ⁻⁵ Torr, an arc current of 100 A, a base material of titanium, a base material bias voltage of 20 V, and a deposition time of 15 seconds.

  Next, after the first metal layer 2 on which the titanium film was formed was washed with acetone, a photoresist made of an acrylic resin was applied on the surface of the titanium film and dried at 90 ° C. for 15 minutes.

Subsequently, a network-like exposure film mask in which the exposed portion was 3% of the surface area of the niobium foil was aligned, and the photoresist was exposed (exposure conditions: 100 mV / cm ² , 30 sec).

  Thereafter, the first metal layer 2 was dipped in xylene and then dried, thereby removing the non-photosensitive portion of the photoresist and exposing the titanium layer.

  This was immersed in a 2 mol / l sulfuric acid aqueous solution to remove the exposed titanium by wet etching. Further, by removing the remaining photoresist, the second metal layer 3 having a plurality of quadrangular regions was produced.

  In order to investigate the area ratio of the region of the first metal layer covered with the second metal layer, the surface of the anode 1 was fabricated using EPMA (Electron Probe Micro-Analysis). Were analyzed by elemental mapping of titanium and niobium. As a result, the portion covered with titanium was 3% with respect to the total surface area of titanium and niobium.

  The anode 1 was anodized in a 1 wt% phosphoric acid aqueous solution at 60 ° C. for 30 minutes at a constant voltage of 10 V to form a dielectric layer 4 having a thickness of 25 nm.

  In this way, a capacitor element 10 (sample name: A1) composed of the anode 1 and the dielectric layer 4 was produced.

(Example 2)
Photoresist exposure using an exposure film mask whose exposed portion is 0.3%, 0.5%, 1%, 5%, 10%, 13%, 15% of the surface area of the niobium foil. A capacitor element 10 (sample names are A2, A3, A4, A5, A6, A7, and A8, respectively) was produced in the same manner as in Example 1 except that the above steps were performed.

  For these capacitor elements, as in Example 1, the surface of the anode 1 was analyzed using EPMA by elemental mapping of titanium and niobium using EPMA. They were 0.3%, 0.5%, 1%, 5%, 10%, 13%, and 15%, respectively.

(Comparative Example 1)
A capacitor element 10 (sample name: X1) was produced in the same manner as in Example 1 except that a niobium foil that was not coated with titanium was used instead of using a niobium foil that was partially coated with titanium. .

(Comparative Example 2)
In a 5 L reaction vessel, 1.5 kg each of potassium fluoride and potassium chloride was added, and the temperature was raised to 850 ° C. to obtain a melt. A nozzle was inserted into this melt, and nitrogen gas was bubbled at a flow rate of 750 mL / min and introduced into the melt. A niobium foil having a thickness of 100 μm was inserted into the melt, and after 1 minute, 5.8 g of dissolved sodium was added and reacted for 2 minutes. And this operation was repeated 30 times, and the niobium anode which added nitrogen was produced. A capacitor element 10 (sample name: X2) was produced in the same manner as in Example 1 except for this operation.

(Evaluation)
The leakage current of the capacitor element produced as described above was measured. FIG. 3 is a schematic diagram for explaining a method for measuring leakage current. In the measurement, as shown in FIG. 3, each capacitor element 10 is immersed in a 1 wt% phosphoric acid aqueous solution 22 placed in a metal container 21, and the dielectric layer 4 is not formed at one end of the capacitor element 10. The measurement anode 23 is connected to the region, the measurement cathode 24 is connected to one end of the metal container 21, the measurement anode 23 and the measurement cathode 24 are connected to an ammeter 25 and a DC power supply 26, and a voltage of 3 V is supplied by the DC power supply 26. Was measured by measuring the current value after 20 seconds.

Table 1 shows the results of measuring the leakage current of each capacitor element.

  As can be seen from Table 1, the leakage current of Comparative Example 2 using a niobium foil added with nitrogen is lower than that of Comparative Example 1 using a niobium foil not coated with titanium. In Example 1 and Example 2 using the foil, the leakage current is further reduced. Samples A1, A3, and A4 using the samples of Example 1 and Example 2 whose anodes covered 0.5% or more and 10% or less of the total surface area of niobium and titanium. , A5, A6 leakage current is significantly reduced.

  If it is less than 0.5%, the effect of reducing the oxygen concentration in the first metal layer made of niobium is considered to be relatively small. On the other hand, if it exceeds 10%, the surface area of the second metal layer made of titanium is increased, and the leakage current through defects formed on the surface of the second metal layer is increased. It is possible to suppress the occurrence of defects in the first metal layer and to cause defects on the surface of the second metal layer, so that the effect of reducing the leakage current as a whole is considered to be small. Therefore, when it is 0.5% or more and 10% or less, the effect of reducing the leakage current can be obtained more effectively.

  It was found that the area of the first metal layer covered with the second metal layer is preferably 0.5% to 10% of the surface area of the first metal layer.

  Next, the relationship between the metal material constituting the second metal layer and the leakage current was examined.

(Example 3)
A capacitor element 10 (sample names are B1 and B2, respectively) was produced in the same manner as in Example 1 except that zirconium and hafnium were used instead of titanium as the metal material constituting the second metal layer. .

  As for the capacitor element of Example 3, as in Example 1, the surface of the anode 1 was analyzed by EPMA and analyzed by elemental mapping of zirconium (B1) or hafnium (B2) and niobium. As a result, zirconium (B1) or hafnium was analyzed. The coating part by (B2) was 3% with respect to the total surface area of zirconium (B1) or hafnium (B2) and niobium.

Table 2 shows the results of measuring the leakage current of each capacitor element.

  As can be seen from Table 2, Comparative Example 1 in which the first metal layer is not covered with the second metal layer also when zirconium or hafnium is used as the second metal layer material in the same manner as when titanium is used. And the leakage current is remarkably reduced as compared with Comparative Example 2.

  Subsequently, the relationship between the metal material constituting the first metal layer and the leakage current was examined.

Example 4
A capacitor element 10 (sample name: C1) was produced in the same manner as in Example 1 except that tantalum was used instead of niobium as the material constituting the first metal layer.

(Example 5)
In this example, niobium was used as a material constituting the first metal layer, and anodization was performed with 1.5 wt% ammonium adipate aqueous solution using aluminum instead of anodizing with 1 wt% phosphoric acid aqueous solution. A capacitor element 10 (sample name: C2) was produced in the same manner as in Example 1 except for.

(Comparative Example 3)
A capacitor element 10 (sample name: X3) was prepared in the same manner as in Comparative Example 1 except that a tantalum foil not coated with titanium was used as the anode 1 instead of using a niobium foil not coated with titanium.

(Comparative Example 4)
Instead of using niobium foil not coated with titanium as anode 1 and anodizing in 1 wt% phosphoric acid aqueous solution, anodizing with 1.5 wt% ammonium adipate aqueous solution using aluminum foil not coated with titanium as anode Except for this, a capacitor element 10 (sample name: X4) was produced in the same manner as in Comparative Example 1.

  As in Example 1, the capacitor elements of Examples 4 and 5 were analyzed by element mapping of titanium and tantalum (C1) or aluminum (C2) on the surface of the anode 1 using EPMA. Both were 3% of the total surface area of titanium and tantalum (C1) or aluminum (C2).

Table 3 shows the results of measuring the leakage current of each capacitor element.

  As can be seen from Table 3, the first metal layer is not covered with the second metal layer in the case of using tantalum or aluminum as in the case of using niobium as the first metal layer material. And the leakage current is remarkably reduced as compared with Comparative Example 4.

  Next, the relationship between the form constituting the first metal layer and the leakage current was examined.

(Example 6)
(Step 1)
Using 0.99 g of niobium powder as the metal constituting the first metal layer and 0.01 g of titanium powder as the metal constituting the second metal layer, the mixture was mixed for 4 hours with a planetary ball mill using cemented carbide balls. A uniformly dispersed powder was obtained. The obtained powder and niobium lead wire were press-molded at the same time to produce pellets. Subsequently, the prepared pellets were sintered at 1100 ° C. under reduced pressure (3 × 10 ⁻⁵ Torr) to obtain a sintered body in which a part of the niobium surface was coated with titanium.

  In order to examine the ratio of the area of the region on the first metal layer covered with the second metal layer for the anode 1 thus manufactured, the anode 1 passes through one arbitrary point on the anode 1 and a shown in FIG. Cross sections parallel to the respective surfaces b and c were observed with a scanning electron microscope (SEM). Thereby, as a result of calculating the coating | coated part with titanium, it was 3% with respect to the total surface area of titanium and niobium.

(Step 2)
The anode 1 was anodized in a 1 wt% phosphoric acid aqueous solution at 60 ° C. at a constant voltage of 10 V for 10 hours to form a dielectric layer 4 having a thickness of 25 nm.

  In this way, a capacitor element 10 (sample name: D1) composed of the anode 1 and the dielectric layer 4 was produced.

(Comparative Example 5)
In Example 6 (Step 1), instead of using a sintered body in which the niobium surface is coated with titanium, niobium powder and niobium lead wire are press-molded at the same time to produce pellets, and in vacuum (3 × 10 ⁻⁵ Torr) ) A capacitor element 10 (sample name: X5) was produced in the same manner except that the niobium sintered body sintered at 1100 ° C. was used as the anode 1.

Table 4 shows the results of measuring the leakage current of each capacitor element.

  As can be seen from Table 4, as in the case of using the metal foil as the first metal layer, when the sintered body is used, the first metal layer is more than the comparative example 5 that is not covered with the second metal layer. Leakage current is significantly reduced.

  As described above, according to the capacitor element according to the above embodiment, the leakage current of the capacitor can be reduced.

  Therefore, according to the solid electrolytic capacitor according to the present invention using the capacitor element according to the above embodiment, the leakage current can be reduced.

  In addition, it should be thought that the Example disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes meanings equivalent to the scope of claims for patent and all modifications within the scope.

  For example, in the above embodiment, the electrolyte layer 5 is made of polypyrrole, but the present invention is not limited to this, and other conductive polymers may be the main component, or manganese oxide may be the main component. Good.

  Moreover, in the said Example, although the 1st metal layer was comprised from niobium, a tantalum, or aluminum, this invention is not restricted to this, The alloy etc. which have these valve action metals as a main component may be sufficient. .

  In the above embodiment, phosphoric acid aqueous solution or ammonium adipate aqueous solution was used for anodic oxidation of anode 1, but the present invention is not limited to this. For example, ammonium fluoride aqueous solution, potassium fluoride aqueous solution, sodium fluoride An aqueous solution containing fluorine such as an aqueous solution and a hydrofluoric acid solution, sulfuric acid, or the like may be used.

It is sectional drawing of the solid electrolytic capacitor by embodiment of this invention. It is a top view for demonstrating the structure of the anode of the solid electrolytic capacitor by embodiment of this invention. It is a schematic diagram for demonstrating the system for measuring the leakage current of a capacitor | condenser element. It is a figure for demonstrating the observation method of the anode 1 by a scanning electron microscope (SEM).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode 2 1st metal layer 3 2nd metal layer 4 Dielectric layer 5 Electrolyte layer 6 Cathode 6a 1st conductive layer 6b 2nd conductive layer 7 Anode terminal 8 Cathode terminal 9 Exterior body 10 Capacitor element 11 Anode lead 12 Conductive adhesion Agent layer

Claims (1)

In a solid electrolytic capacitor including an anode, a cathode, and a dielectric layer formed by anodizing the anode, the anode is made of niobium, aluminum, or tantalum, or niobium, aluminum, or tantalum. A first metal layer made of an alloy as a main component, and a part of the surface of the first metal layer is coated with a second metal layer containing any of titanium, zirconium, and hafnium ;
The area of the area | region of the said 1st metal layer coat | covered with the said 2nd metal layer is 0.5 to 10% of the surface area of the said 1st metal layer, The solid electrolytic capacitor characterized by the above-mentioned.

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